1. Field of the Invention
The present invention relates to a multi-processor system composed of a plurality of processors and a method of communication among processors, and more particularly to a multiprocessor system and a method of communication among processors suitable for a terminal system handling multi-media.
2. Description of the Related Art
Conventionally, in a system for processing images or the like, it has been aimed at to make processing high in speed by using a plurality of exclusive processors instead of performing all image processings in one processor. This is evident, for example, from Japanese literature "Video Information (1)" 1987/12 pp. 23 to 27 "Up-to-Date Image Processing Work Station VICOM-VME Series" for instance. In this case, transmission and reception of data among exclusive processors are performed through an exclusive bus provided separately from a general system bus, and, a method of preventing degradation caused by data traffic other than image processing has been adopted.
In the example described in the abovementioned literature, it is aimed at to make data transfer high in speed by preparing a plurality of processors exclusive for image processing and using a bus IMAGE-BUS exclusive for image processing data which is different from a system bus VME-BUS for communication among these exclusive processors.
The above-mentioned related art has had problems mentioned below since the communication channel exclusive for image processing is in the form of a bus.
Namely, it is required to acquire the right of using a bus in order to commence communication among processors, and, while another processor is performing data transfer, commencement of communication has to be kept waiting until data transfer is ended. Thus, in the case where real time performance is required, e.g., in the case of multi-media information such as a voice or an image, there has been such a problem that the real time performance of the media becomes no longer be warrantable because of delay in processing due to waiting time until the right of using a bus is acquired.
Further, in the above-mentioned related art, communication only between one set of processors can be performed simultaneously. Therefore, when it is intended to prevent the bus from being occupied by a specific processor, continuous use time of the bus allowed for respective processors has to be restricted, and when a processor is going to send comparatively long data, one transmission data stream is cut in pieces once during transmission. There has been such a problem that isochronism of the information is lost due to a fact that time base control is not being made in restoring processing in the processor on the receiving side.
Furthermore, communication can be performed simultaneously only between one set of processors according to the above-mentioned related art adopting bus connection. Therefore, there has been also a problem that processing operation by means of a plurality of processors such that an image input processor transfers image data inputted from a camera to an image processing processor while a communication processor is transferring data received from a network to a file processor, or the result of processing by the image processing processor is transferred to an image display processor in parallel with those operations cannot be performed in parallel.